After it premiered on May 31st, Tomb Raider's debut "Crossroads" game-play trailer was later awarded "Best New Trailer" by IGN's Best of E3 2012 Awards.
The music that features in the trailer consists of presumably a third party cue, followed by possibly in-game pieces by the unannounced composer for the game, contiguous with a tailored edit of trailer score company RipTide Music's licensed piece, "Thermal Shock", by composer Cliff Lin. Starting at 2:14 and resuming at 2:54, the rock-influenced "Shock" is cut surrounding a definite reiteration of the new Tomb Raider theme.
Sampled below, the track was made purchasable in March, 2012, via iTunes and Amazon MP3, in Lin's compilation album "This is War":
Thermal Shock [Excerpt]
Update: The beginning trailer score has been identified as "Paradigm Shift" by music powerhouse Groove Addicts from the promotional license album Full Tilt - Convergence. It is currently not commercially available.